Colour tag checker
Why does my export look washed out?
A video file says which colour space it’s in with a few small tags, and every player and platform reads them a little differently. Drop in an export or a phone clip to see its tags, how Chrome, Safari and QuickTime will show it, what YouTube and Vimeo will do with it, and which export setting changes it.
Drop an export or a phone clip (MP4 or MOV)
Only the file’s headers and first frame are read, so a long 4K export takes a second. Nothing is uploaded.
The gamma shift, measured
The same BT.709 export looks lighter and flatter in Safari and QuickTime than in Chrome. We measured it: a mid grey drew at 141 in Safari and QuickTime and 130 in Chrome, a dark grey at 64against 56. Apple applies the BT.709 transfer when it shows the file; Chrome doesn’t. Re-tagging doesn’t avoid it. The commonly suggested “1-2-1” tag drew exactly like “1-1-1” in all three, and so did an untagged file. Only the sRGB transfer tag made Safari match Chrome, and YouTube converts that one. So it isn’t a broken export. It’s a choice of which screen to grade for, and Premiere and Resolve both have a setting for it.
One tag does split the players in opposite directions: gamma 2.8, the old PAL tag, which Premiere Pro wrote on a standard-definition PAL export we checked. Chrome drew its mid grey darker (109) and Safari lighter (148).
Two places, two answers
Tags live in the container (the MP4 or MOV’s colr box) and in the video bitstream itself. Chrome reads only the bitstream; Safari and QuickTime read the container first. So when the two disagree, usually because a file was re-wrapped or re-tagged after export, or when only the container is tagged, as some Apple apps and Android phones write it, the same file can show different colours in each.
Phone HDR
iPhones record HLG and Dolby Vision. Tagged, players recognise it and tone-map it for SDR screens. When the tags are lost (an app re-encodes it, or an export keeps the HDR picture but writes SDR tags), every player we measured showed it as plain SDR: lifted shadows and a flat, grey picture. The checker spots the HDR signs a file still carries (mastering metadata, light levels, a Dolby Vision record, 10-bit BT.2020) when its tags say SDR.
Where the claims come from
YouTube publishes how it handles colour tags and what HDR must look like; Vimeo publishes its HDR requirements; Instagram and TikTok publish nothing on colour, and this page says so rather than repeating blog posts. How the players behave isn’t published anywhere, so we measured it with test files of known tags, decoded in each player and read back pixel by pixel. Each result shows the app, the OS and the date.
Related: YouTube upload checker · one export, three platforms · more tools for creators · for broadcast and VOD masters, the HDR metadata checker.